The present invention relates to a positioning element system in which a positioning element is provided formed of at least two piezo-electrical bodies each formed of a plurality of lamellae provided with electrodes. The lamellae extending in a motion direction of the positioning element are mechanically connected to one another with their principle surfaces parallel to the direction of motion so as to be immobile with respect to one another. Upon application of an electrical voltage with a field direction which promotes a polarization of the material of the lamellae, the body is shortened.
In the earlier German patent application No. P 30 40 563.1 (VPA 80P7188), incorporated herein by reference, a positioning or control element is disclosed with a piezo-electrical body as the transducer. This piezo-electrical body consists of a plurality of lamellae consisting of piezo-ceramic material, the principal surfaces of said lamellae being connected surface-wide to one another and immobile with respect to one another, whereby the length of the individual lamellae and thus of the entire body is at least 5 times as great as the thickness of the individual lamella. The lamellae all have the same thickness.
In a simple embodiment of such a body a plurality of such piezo-ceramic lamellae (each individually provided on its principal surface with a metallization as a electrode) are bonded to one another across their respective principal surfaces. This plurality of lamellae thus forms a mechanically stable bar or the like. The aforementioned metallizations have electrical terminals which lead to the outside. All lamellae are electrically connected in parallel to a controllable, electrical excitation voltage.
Depending on the height of the electrical excitation voltage, a piezo-electrically effected change of length of the body constructed of lamellae is produced. Because of the operational sign of the piezo-electrical coefficient D.sub.31, a shortening of this laminated body is produced when an electrical voltage is applied whose field direction in the piezo-ceramic material of the individual lamella promotes the impressed polarization which exists there. One obtains an electrically effected elongation or lengthening of this laminated body when, after a preceding electrical charging (by voltage as specified above) of the lamellae of the body which form the electrical capacitances, one short-circuits all of said lamellae, i.e., allows these capacitances to discharge. The body which had been previously shortened due to electrical forces in its charged condition then quickly re-expands to its original length in its neutral condition.
For the sake of completeness, let it be noted that a positioning element consisting of a stack of tablets of piezo-ceramic material lying on top of one another in which the D.sub.33 piezo effect is exploited has the opposite behavior. For example, this tablet stack experiences an elongation in the direction perpendicular to the principal surface of the tablets (i.e. in its stack height) when one again applies an electrical voltage to the individual tablets which promotes the polarization direction of the piezo-ceramic of the tablets.
A proposal has already been made to employ a tablet stack as described above in a positioning element combined with at least two laminated bodies consisting of piezo-ceramic as described above. The tablet stack and the laminated bodies are positioned adjacent to one another in such manner that the tablet stack lies between at least two laminated bodies. The tablet stack and the laminated bodies are connected to one another by means of a mechanically stable cross arm at their respective one adjacent end. When the respective opposite ends of at least the two outside laminated bodies are connected to the mass, for example to the housing or frame of a machine or the like, then the adjacent end of the tablet stack is the active end of such a positioning element. Accordingly, for example a valve or the like can be controllably actuated (with respect to the housing or frame of the machine). Because of the D.sub.31 effect in the laminated bodies and of the D.sub.33 effect in the tablet stack, a resultant dilation or expansion motion of said positioning element is produced given the parallel electrical connection of the laminated body and of the tablet stack for an applied electrical voltage with a direction of its field which promotes the impressed polarization.
Prior art relating to piezo-electrically actuated positioning elements include the publications German Letters Pat. No. P 17 98 339; Fienwektechnik und Messtechnik, Volume 87 (1979), pages 181-183; and Industrial Research Magazine, Volume 4 (1978), page 500, all incorporated herein by reference.